Total RNA samples typically contain RNA molecules that vary in length. For example, a total RNA sample obtained from mammalian cells may contain mRNA molecules (which generally range in size from a few hundred bases to several kb), lincRNA molecules (which are classified as being at least 200 bases in length), 18S and 28S rRNA molecules (which are approximately 1.9 kb and 5 kb, respectively), tRNA molecules (which are generally below 100 nt in length), and a variety of small RNA molecules (e.g., short interfering RNAs, microRNAs, tiny non-coding RNAs and small modulators RNAs) many of which are less than 30 nucleotides in length.
Conventional methods for sequencing the mRNAs and small RNAs in the same sample typically involve two workflows, one for the mRNA and the other for the small RNA. Such methods can be cumbersome.